northstar :: program writeups :: VALDEZ

DYNACOMP

NORTH STAR

DYNACOMP P.O. BOX 162 WEBSTER N.Y. 14580

DYNACOMP © 197 9

P.O. BOX 162

WEBSTER, N.Y. 14580

VALDEZ - A SUPERTANKER SIMULATION
VERSION 2.0

VALDEZ is a microcomputer simulation of supertanker navigation in the Valdez
region of Alaska. See the attached figure. Valdez is terminal port for the Alaskan
oil pipeline. To get to Valdez harbor, supertankers must enter Prince William Sound
from the North Pacific and cross that body of water to Valdez Narrows. Crossing this
sound is complicated by the presence of islands, moving icebergs, and other
supertankers heading for the North Pacific. Valdez Narrows itself is very treacherous
as the passage is only 900 meters wide. Careful maneauvering (in the presence of
tides) is required.

The program carefully simulates the above real life features of supertanker
navigation in the following ways:

1) The movement of the supertanker under your control is simulated through
equations which describe the effects of drag, inertia and engine performance.

2) A detailed map of the Prince William Sound area is stored bit-wise in the
computer's memory.- The storage is fairly efficient and covers a 256 by 256 element
grid. Tne spacing between the grid points is 500 meters. Included on this grid are
the coastline and islands as they appear on a recent Rand-McNally map.

3) The passage to Valdez is complicated by the presence of icebergs which
originate from the Columbia Glacier. These icebergs are included in the simulation.
Their motion is governed by the tides.

4) The tidal patterns of the Prince William Sound area are also simulated
both with respect to time and position. These tides must be particularly reckoned
with when entering the Narrows as there is not much room for error.

5) Other supertanker traffic is included. This traffic consists of several
ships following a course from Valdez to the Pacific. This on-coming danger is
particularly acute within the Narrows and harbor area.

Operation of the simulation is straight-forward. Most of the prompts are
self-explanatory. The reader is referred to the attached annotated run listings for
examples. However, to avoid confusion, a few of the responses will be discussed here.
Observe that there is also an "instructions" option when running the program in the
full version (17 kilobytes for the program plus 8 kilobytes for the map).

Because the map is very detailed (256 by 256), it is stored in the computer's
memory in a bit-wise manner. The map is located outside the program space used by
BASIC. This means that the usual practice of setting the user memory size to the
maximum available must not be followed. Where this map memory space is to reside
depends on the memory bound set by the user. In the North Star BASIC case, one can
use the memory above BASIC by responding to "WHERE IS THE MAP TO BE STORED IN MEMORY
(DECIMAL): ?." with a value one greater than the MEMSET number given earlier (see the
sample run listing). For example, if the top of memory was set to 48000 via the
MEMSET command, then the map storage could start at 48001. Note that the map requires
8 kilobytes of memory! The map may also be stored starting at location in memory.
This would use the entire region in front of the standard location of the DOS. The
program runs perfectly well with the map in that location, but the DOS is affected
and will not save programs properly later. However, the DOS can simply be reloaded
after, exercising the simulation. In summary, the user must decide on where to store
the 8 kilobyte map and must be sure that the region is safe from unintentional
alteration by BASIC. In general, if the program memory boundary can be set 8192 bytes
lower than the maximum available, ithile still leaving enough space to run the
program, there should be no problem.

The simulation can be run in several modes. The program will ask whether or not an
open sea exercise is desired. If the answer is "Y", then a blank map will be loaded
(i.e., no coastline or islands). In this mode one can practice maneuvering the
supertanker. As the other ship and iceberg traffic is overlaid on this map, you can
practice precision navigation in chasing and ramming other ships. This is not an easy
task as the other ships are also moving, and careful navigation is required for
interception. Remember, supertankers do not respond to controls quickly. Large jnasses

do not change direction and speed without considerable effort.

If you answer "N" to the open sea practice simulation question, there is another
decision point. The next question is whether or not the Prince William Sound map
should be loaded. The reason for this question is that you may have ended one round
of simulation and want to start again. Because the map is still in the computer's
memory, there is no reason to reload it. Note that loading the map takes some time
because it is so large. If you answer "Y", the map will be loaded. If instead the
answer is "11", and the VALDEZ map had not been previously loaded, then the radar
display will reflect whatever random patterns there are in the reserved region of
memory. This will often look like many irregularly distributed islands, and can be
used as a map in itself. The objective then would be to not run aground.

If the Prince William Sound map is loaded, some realistic navigation can be
performed. As the map is extensive, you can simply sail around the sound,
circumnavigate islands, travel up fiords, and so on. You can also attempt the
challenge of mooring at Valdez. First you have to get to the harbor. Second you have
to pull up to a floating pipeline terminal located at a particular position. There
are also requirements on the orientation of the tanker at final docking. These
requirements are given in the "instructions" included in the full version of the
program, and also listed separately.

Control of the ship is through the rudder and two engines. The rudder control is
given in degrees (-45 to +15), and the engine power is given in percent. For example,
full ahead would be 100(?), half reverse would be -50(%).V Having two engines comes in
handy in case one breaks down (which can happen!). The prompts for these controls are
self-explanatory, as are the status displays. However, the radar display requires
some discussion.

The simulation behaves as if the fog is very thick and the information is all
electronic. As the. Coast Guard maintains very tight monitoring of the traffic in the
sound, the locations of all other traffic is known fairly accurately. However,
curious as it may be, even when ships see one another, they still manage to collide.
To aid the captain in avoiding collisions and skirting coasts, variable range radar
is supplied. This radar has magnifications of 1x, 2x, 4x, 8x, I6x and 32x. A
magnification of 1 gives the highest resolution and will show everything within
range. A magnification of 32 has a course resolution, but will display the entire map
(the region outside the map is shown as land). You will find that the various
magnifications are very useful. Note that responding to the radar range factor prompt
with a "0" will skip the plot. Skipping the radar display is often desirable as it
takes some time to print; it is 16 by 16 grid elements, and the map must be unraveled
from memory.

The display portions of the simulation were designed to be compatible with
terminals having line widths of 32 or more characters. This placed a limit on the
size of the radar display. For those with wider terminals, the appropriate change can
be made in the FOR/NEXT loop arguments in the radar display subroutine. This might be
desirable since for radar range factors larger that 1 , there is a strong possibilty
that other ship and iceberg traffic will be missed because of the reduced resolution.

In running the simulation, most of the execution time is spent calculating the
ship and iceberg movements. The motion is calculated in ten iterative steps. During
periods of excitement, the delay becomes particularly apparent. However, if you
consider the number of calculations performed, as well as the completeness of the
simulation, the time gap is really not that great.

Additional comments:

The computer map is square and laid out in the following way. The lower left
corner is designated as the origin. Its coordinates are X=0 kilometers and Y=0
kilometers. The upper right hand corner is at X=127.5 kilometers and Y=127.5
kilometers. Up is North; right is East. The supertanker starts its simulated course
at X=125 kilometers, Y=6. This is very close to the lower right corner. The initial
course direction is -45 degrees off North, which is Northwest. This course is in the
direction of Hinchinbrook Entrance, but not exactly. Some course correction is
required to accurately enter the passage. Once within the pass, a due North course is
advised. This will bring the ship into the vicinity of Valdez Arm, which leads to the
Narrows and thence to the port. A considerable amount of navigation is necessary to
pass through the arm to the port. The final mooring coordinates are X=108 kilometers
and Y=123 kilometers.

Valdez

Wei Is Passage

BHgh I

. Naked I.

Perry I.

Red Head

PRINCE WILLIAM SOUND

"Hinchinbrook
I.

GULF OF
ALASKA

Montague I .

NORTH PACIFIC

VALDEZ map as contained in the computer's memory. The actual map is square with
256 grid elements on a side. The display above was created by printing the memory
contents as blanks (for "0") and asterices (for "1"). Lines of asterices give the
appearance of TV raster lines, and indicate the resolution provided in the
simulation.

'VALDEZ* IS A COMPUTER SIMULATION OF SUPERTANKER TRAFFIC
IN THE PRINCE WILLIAM SOUND AREA OF ALASKA. THE OBJECT OF
THE SIMULATION IS TO MANEUVER A LARGE SUPERTANKER THROUGH
THE SOUND AND VALDEZ NARROWS TO AN OIL PIPELINE TERMINAL AT
VALDEZ.

THE SIMULATION IS COMPLICATED BY SEVERAL REALISTIC PROBLEMS.
FIRST, A DENSE FOG IS ASSUMED. THIS REQUIRES ALL NAVIGATION
TO BE PERFORMED USING COMPASS HEADINGS AND RADAR DISPLAYS.
THE RADAR DISPLAY IS MULTIPLE RANGE AND IN THE SHORT RANGE
SETTING HAS A RESOLUTION OF 500 METERS. THIS RESOLUTION IS
PARTICULARLY IMPORTANT IN PASSING THROUGH THE NARROWS WHERE THE
LEEWAY IS ONLY 900 METERS. ANOTHER DANGER IS OTHER
SEA TRAFFIC, INCLUDING BOTH SHIPS AND ICEBERGS. A CONSIDERABLE
AMOUNT OF SHIPPING IS LEAVING VALDEZ HARBOR AND PASSING
THROUGH THE NARROWS. THIS ONCOMING TRAFFIC MUST BE AVOIDED.
THESE SHIPS FOLLOW A PARTICULAR SEA LANE, BUT THE DEPARTURES
ARE RANDOM. THE ICEBERG TRAFFIC IS REALISTICALLY MORE RANDOM.
THE ICEBERGS ORIGINATE AT THE TIP OF THE COLUMBIA GLACIER
AND ARE SUBJECT TO THE TIDES, WHICH ARE ALSO SIMULATED.
THE ICEBERGS THEREFORE MOVE SLOWLY, BUT CROSS THE SEA LANES.

TWO BASIC CONTROLS ARE AVAILABLE TO THE CAPTAIN. THEY ARE
ENGINE POWER (TWO ENGINES) AND HELM (RUDDER). IT IS ASSUMED
THAT A CONTROLLED HELM IS IN PLACE SO THAT ONCE
THE COMMAND IS SET, IT REMAINS UNTIL INTENTIONALLY ALTERED.

THE SIMULATION IS AN EXERCISE IN PRECISION NAVIGATION.
THE NAVIGATION IS RELATIVE TO A 256 X 256 GRID HAVING 500
METER SPACINGS. ALL DISTANCES ARE IN METERS. THE PORT IS
LOCATED AT GRID POSITION X=108 KILOMETERS (LONGITUDE) AND
Y= 123 KILOMETERS (LATITUDE). FINAL MOORING IS NEXT TO A
FLOATING PIPELINE TERMINAL. THE ANCHOR WILL BE DROPPED
UNDER THE FOLLOWING CONDITIONS:

POSITION: WITHIN 100 METERS OF TERMINAL
HEADING: BETWEEN 80 AND 100 DEGREES OFF NORTH
SPEED: LESS THAN 0.7 KILOMETERS/HOUR

COLLIDING WITH ANOTHER SHIP OR AN ICEBERG ENDS THE SIMULATION.
SO DOES RUNNING AGROUND. A COLLISION REPORT IS GIVEN DESCRIBING
THE DAMAGE.

THE SIMULATION MAY BE EXERCISED IN TWO GENERAL WAYS.
BY CLEARING A PATCH OF SEA WHEN GIVEN THE OPTION YOU CAN
PRACTICE WIDE RANGING MANEUVERS AS WELL AS ATTEMPT TO INTERCEPT
OTHER SHIPS. BY LOADING THE PRINCE WILLIAM SOUND MAP, THE FULL
SIMULATION MAY BE EXERCISED.

REMEMBER, SUPERTANKERS ARE BIG AND SLUGGISH IN HANDLING
CAREFULLY PLAN YOUR COURSE!

Instructions as they are printed out when running the
25 kilobyte version of VALDEZ. The instructions option
has been removed from the compressed versions.

Sample listings for the North Star version of VALDEZ. Other versions ire similar.

MEMSET 31600
READY

LOAD VALDEZC
READY

RUN

Set the memory boundary such that at
least 8K (8192) bytes of memory are free
for map storage, with also 8k available
to run the program. In the example shown
(North Star, using Release k BASIC),
approximately 8100 bytes are available
for the program.

Load the compressed version of VALDEZ.
The full version requires in excess of
17 kilobytes for the program Itself,
and an additional 8 kilobytes for the
map. The compressed versions are built
from the 17K program by removing REM
Statements, blanks, and by concatenating.

VALDEZ - A SUPERTANKER SIMULATION

NORTH STAR VERSION NSCV1.0
COPYRIGHT 1979 BY DYNACOMP
WEBSTER, NEW YORK

Other versions available include
compressions for the 16K Level I I TRS-80
and 16K PET.

SIMULATION BEGINS

INPUT A NO. BETWEEN AND 1000716

WHERE IS THE MAP TO BE

STORED IN MEMORY (DECIMAL): 7 31601

IS THIS TO BE AN OPEN

SEA PRACTICE SIMULATION (Y/N): ?N_

IS PRINCE WILLIAM MAP LOADED (Y/N):
LOADING PRINCE WILLIAM SOUND MAP..,

STATUS

?N

TIME: 9.35 HOURS
POSITION:

125 KM EAST

KM NORTH
WATER SPEED: 18.9 KM/HOUR
TIDE: 1.9 KM/HOUR SOUTH
HEADING : -15 DEGREES OFF NORTH
PORT ENGINE POWER: 75?
STARBOARD ENGINE POWER: 75*
HELM: DEGREES

RADAR RANGE CONTROL

RADAR RANGE FACTOR: ?^2

GRID INCREMENT: 16 KILOMETERS

• • • « •

• • • *

•••••••••

• •••«§*«■

• a. •••!««•

C0NTINUE7Y

DISPLAY OTHER TRAFFIC (Y/N): ?Y_
LAST REPORTED SHIP POSITIONS

1

X= 91.1

Y=

120.1

2

X= 88.5

Y=

116.3

3

X= 79.5

Y =

76.1

1

X= 83. 4

Y =

103.1

5

X* 79.5

Y =

32

6

X* 85.6

Y=

111.7

CONTINUE7Y

LAST REPORTED ICEBERG POSITIONS

This randomizes the distribution of
icebergs and ships.

Input the first free memory location,
■Normally this is one greater than the
memory bound.

If "Y", then a clear patch of sea is
prepared instead of the map.
■ If "Y", the program assumes the map has
already been loaded into the memory
region indicated above. Not clearing the
sea or loading the map will result in a
randomized pattern unless the map had
been loaded in an earlier play.

The supertanker always starts from the

same location (near the lower right of

the map).

South is general; it might be southeast.

Current direction of travel.

The engines supply power additively.

Power can range from -100% to +100%.

Angle of the rudder. When moving forward,

a positive angle corresponds to turning

right.

The navigational display. Open sea is
shown as dots; land, icebergs and other
ships as asterices. The radar range fact-
ors allowed are 0, 1, 2, k, 8, 16 and
32. A "0" input is used to skip the dis-
play. If the supertanker were in the
center of the map, a range factor of 16
would display the map in its entirety.
The area outside the map boundaries is
treated as solid land. In the example
to the left, the upper right hand quad-
rant represents the stored map. The
other three quadrants are outside the map
boundary. The "0" denotes the location
of the supertanker. The radar display
Is always centered on this ship. The
resolution is poor when using high
magnifications. However, some of the
large features shown on the attached
map are apparent in this display.

The "CONTINUE" prompts are designed for
16 line video monitors. The object is to
keep the data from scrolling of the
screen before ft is read.

1

Xs 71 Y« 85.6

- The number of ships and their Initial
locations art chosen according to the
random number generator seed given
above. These ships follow a set course
from Valdez, down the Valdez Arm, across
the Prince William Sound, through the
Hlnchlnbrook Entrance and Into the

Gulf of Alaska.

- The Icebergs drift with the tide.

CONTINUE?*

ENGINE CONTROL

STATUS: PORT 75$ AHEAD
STARBOARD 75$ AHEAD

CONTINUE CURRENT STATUS (Y/N)?Y

RUDDER CONTROL

Engine power can range from -100y: to
+100%. Each engine can be individually
controlled. It is possible for an engine
to fail without warning. Also, engine
carnage occurs with collisions.

STATUS: DEGREES RUDDER

CONTINUE CURRENT STATUS (Y/N)?X

HOW MANY MINUTES IS THIS SPEED
AND HEADING TO BE MAINTAINED: ?30

STATUS

TIME: 9.85 HOURS
POSITION:

117.56 KM EAST

6.91 KM NORTH
WATER SPEED: 21.1 KM/HOUR
TIDE: .5 KM/HOUR SOUTH
HEADING : -15 DEGREES OFF NORTH
PORT EN3INE POWER: 75%
STARBOARD ENGINE POWER: 75$
HELM: DEGREES

— The rudder is controlled by inputting an
angle. 20 degrees left rudder would be
set by answering the question to the left
with "N H , and then responding with "-20"
when prompted.

- "^his is how long the ship will travel before
a new command may be entered. It is as if
the ship controls were set and the captain
went for coffee.

~7ime has increased by 0.5 hours.

-The ship has moved 7.^4 kilometers to the
west, 6.91 kilometers to the north; a total
of about ten kilometers.

- 'iote, the tide is changing slowly.

-Same heading as before. However, note that
ihe heading is relative to the map and the
tide causes the actual course direction to
be a little different.

RADAR RANGE CONTROL

RADAR RANGE FACTOR: ?8_

GRID INCREMENT: 4 KILOMETERS

— A good value for long range scanning.

, » * ..»»»»»

C0NTINUS7Y

The lower left part of Hinchinbrook
Island is visible. The entrance to the
sound is on the far side of this. The
present course is at 45 degrees and inter-
sects this arm. A course change will be
necessary.

Note that the supertanker has moved on the
rap. This can be seen relative to the map
boundary.

If there were other ship traffic within the
field of view of the radar, it would have
one chance in sixty-four (8x8) of being
displayed because of the low resolution.

DISPLAY OTHER TRAFFIC (Y/N): ?JY
LAST REPORTED SHIP POSITIONS

Xr 86.3

X = 83.7

X = 79.5

X= 79.5

X= 79-5

X= 80.8

Y= 112.1
Y= 108.7
Y= 67.1
Y= 100.3

Y= 23-"

Y= 104.1

CONTINUE?*

LAST REPORTED ICEBERG POSITIONS

'»ote that this ship has moved about five
kilometers to the west and about eight to
the south. It is travelling down Valdez Arm.

-'his ship has moved nine kilometers south.
it is exiting the Hinchinbrook entrance and
heading into the Gulf of Alaska.

1

70.9 Y= 85.2

-The iceberg has moved south Q.k kilometers.

CONTINUE? Y

STATUS

A different example showing a collision

TIMS: 9.37 HOURS
POSITION:

79.32 KM EAST

71.3 KM NORTH
WATER SPEED: 19 KM/HOUR
TIDE: .5 KM/HOUR SOUTH
HEADING : 5 DEGREES OFF NORTH
PORT ENGINE POWER: 75*
STARBOARD ENGINE POWER: 75*
HELM: 5 DEGREES RIGHT RUDDER

Ship Is located between Naked Island
and Red Head; open water.

Course almost due north. A course correct-
Ion had been made recently In order to
head more directly Into Valdez Arm.
Still In the process of correcting course.

RADAR RANGE CONTROL

RADAR RANGE FACTOR: ?1

GRID INCREMENT: .5 KILOMETERS

Maximum resolution Is used here as there is
likely to be other shipping in the area.

CONTINUE?!

DISPLAY OTHER TRAFFIC (Y/N): ?Y_
LAST REPORTED SHIP POSITIONS

■Something has appeared on the radar display.
Since we know that the current supertanker
location is in open water, the radar target
is either another ship or an iceberg.

■According to the display, the target is
ahead about 1.5 kilometers.

X= 90.9
X= '88.3
X= 79.5
X= 83.2
X= 79.5
X= 85.4

Y= 120.2
Y= 116
Y= 75.8*
Y= 107.9
Y= 31.7
Y= 111.4

CONTINUE7Y

LAST REPORTED ICEBERG POSITIONS

-This is the other ship. This is determined
by cocoa ring the position of our ship as
given under "STATUS" above with the posi-
tions on this list. Ship #3 is ahead
1.5 kilometer north, 180 meters east. We
are heading right for it!

X= 71 Y= 85.6

CONTINUE7Y

ENGINE CONTROL

STATUS: PORT 75* AHEAD
STARBOARD 75? AHEAD

CONTINUE CURRENT STATUS (Y/N)?Y

RUDDER CONTROL

There is also an iceberg roughly fifteen
kilometers away.

STATUS: 5 DEGREES RIGHT RUDDER

CONTINUE CURRENT STATUS (Y/N)?_Y

HOW MANY MINUTES IS THIS SPEED
AND HEADING TO BE MAINTAINED: ?J5_

ItlllllllltllilllitKKil

COLLISION WITH SUPERTANKER 111

•••MAJOR COLLISION*"*

TAKING ON WATER

ENGINE STATUS FOR PUMPING:

PORT: 34*

STARBOARD: 0*
PUMP POWER INSUFFICIENT. SINKING.
READY

No change. We are going to see what happens
when there Is a collision.

■The other ship is travelling south at 1U
kilometers per hour (slow because it Is
loaded), and we are travelling north at
19 kilometers per hour. The impact speed
will be 33 kilometers per hour and occur
in less than two minutes. •

A considerable amount of engine power has
been lost; too much. The pumps can not
keep up.

Successful mooring example. Getting to t k i s position is difficult.

STATUS

TIME: 9.35 HOURS
POSITION:

107.8 KM EAST

123-19 KM NORTH
WATER SPEED: .7 SM/HOUR
TIDE: .5 KM/HOUR SOUTH
HEADING : 85 DEGREES OFF NORTH
PORT ENGINE POWER: 0%
STARBOARD ENGINE rOWER: 0%
HELM: DEGREES

■The object is to get to the mooring position
which is located at X«=I08 kilometers (north),
Y«I23 kilometers (east).

-This is the maximum speed at which the anchor
may ae dropped. Some headway must be main-
tained as there Is a tide to be overcome.

•The tide is actually toward the south- south-
west (SSW).

RADAR RANGE CONTROL

RADAR RANGE FACTOR: ?J_

GRID INCREMENT: .5 KILOMETERS

1 » • » * *

» • * » » *
• *

• ••••»*

• **•*»*

• •••••

C0NTINUE7Y

« •

* •

* *

* c

* *

« «

* *

* c

* •

* »

«

* * • * «

■Here is a chance to get a view of the east
end of vaidez harbor area. Compare this with
the nap.

Compare the scale here with the attached map.
Other areas which offer interesting challenges
in navigation are Wells Passage and Montague
Strait. Getting into the hook in Hinchinbrook
Island (off Hinchinbrook Entrance) is
difficult, as are some of the fiords.

DISPLAY OTHER TRAFFIC (Y/N):
C0NTINUE7Y

?N

No need to check on other traffic. None is
visible on the radar display.

ENGINE CONTROL

STATUS: PORT STOPPED

STARBOARD STOPPED
CONTINUE CURRENT STATUS (Y/N)?Y

RUDDER CONTROL

This is a tricky choice. If forwards engines
are used, the mooring speed will be exceeded.
If reverse engines are used, there may not
be enough headway against the tide. In any case
the nooring position is only a few hundred
meters off.

STATUS: DEGREES RUDDER

CONTINUE CURRENT STATUS (Y/N)?N_
HELM CONTROL (DEGF2ES): ? -30

HOW MANY MINUTES 13 THIS SPEED
AND HEADING TO BE MAINTAINED: ?3

- A feeble attempt is made to turn into the tide.

STATUS

TIME: 9.H HOURS
POSITION:

107.82 KM EAST

123. 16 KM NOFTH
WATER SPEED: .7 KM/HOUP
TIDE: .5 KM/HOUR 30UTH
HEADING : &b DEGRfcZS OFF NORTH
PORT ENGINE POWER: 0%
STARBOARD ENGINE FOWER: 0%
HELM: 30 DEGREES LEFT RUDDER

Note th*t the tide has carried the ship 30
meters south while the headway was only 20

meters.

Travelling so slow, we can not expect the left
rudder to have much effect.

RADAR RANGE CONTROL

RAOAR RANGE FACTOR: ?0

DISPLAY OTHER TRAFFIC (Y/N): ?N_
CONTINUE7Y

ENGINE CONTROL

No point In displaying; there has been nearly
no change In position.

STATUS: PORT STOPPED

STARBOARD STOPPED
CONTINUE CURRENT STATUS (Y/N)?Y

RUDDER CONTROL

STATUS: 30 DEGREES LEFT RUDDER

CONTINUE CURRENT STATUS (Y/N)?_Y

HOW MANY MINUTES IS THIS SPEED
AND HEADING TO BE MAINTAINED: ?20

DROP ANCHOR! !!

OIL DEBARKATION POSITION REACHED

SAFELY. CONGRATULATIONS.

TIME IS 9.74 HOURS

The only thing to do now Is to drift into the
mooring area.

We made it*.

READY

RADAR RANGE CONTROL

RADAR RANGE FACTOR: ?J_

GRID INCREMENT: .5 KILOMETERS

An example of "ghosts"

Ghosts are mysterious small islands which
appear after the simulation has been run more
than once without loading in a "fresh" map.
What' happens is that when a simulation has ended,
either by collision or successful mooring, the
iceberg and ship markers are not removed and
show up as land on the next map unless a new
map Is loaded. For example, of the two images
shown to the left, one represents a moving
ship while the other is a ghost. Which is
which?

C0NTINUE7Y

DISPLAY OTHER TRAFFIC (Y/N): ?J_
LAST REPORTED SHIP POSITIONS

1

X= 90.8

Y= 119.9

2

Xs 88.2

Y= 115.7

3

Xr 79.5

Y= 75.4

M

Xs 83

Y= 107.6

5

. X* 79.5

Y= 31.4

6

X* 85.3

Y= 111.1

C0NTINUE7Y

LAST REPORTED ICEBERG POSITIONS

Which of these ships (if any) corresponds to
the radar Images above?

To find out you can:

1) Compare your location against the
radar display and ship location
list.

2) See which one Is stationary (land).

3) Run one down to see what type of
collision has occurred.

1

X« 71 Y« 85.6